Surprise! Being exposed to more music makes you more likely to buy more music...

However, our analysis of the Canadian P2P file-sharing subpopulation suggests that there is a strong positive relationship between P2P file-sharing and CD purchasing. That is, among Canadians actually engaged in it, P2P file-sharing increases CD purchasing.
Intellectual Property Policy Directorate - The Impact of Music Downloads and P2P File-Sharing: Summary of findings

And perhaps more astounding is the fact that people who like music buy more albums than people who don't!

Regarding music taste, we find that people who declare that they have a 'very strong interest' or 'somewhat strong interest' in music compared with people who declared that they had a 'very low interest' in music purchased significantly more CD albums.

The survey is refuted here, specifically relating to the first claim above - I suspect no one in their right mind would take a chance on refuting the second claim!